For much of the earliest history of our species, home may have been nothing more than a small fire and the light it cast on a few familiar faces, surrounded perhaps by the ancient city-mounds of termites. [But] homesick children know how sharp the boundary between home and not-home can be because they suffer from the difference, as if it were a psychological thermocline. I know because I was one of them. I felt a deep kinship almost everywhere in the small Iowa town I grew up in. But spending the night away from home, at a sleepover with friends, made every street, every house seem alien. And yet there was no rejoicing when I got back home in the morning. Home was as usual. That was the point. . .